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Cullars Rotation

Charles Mitchell, Auburn University

Cullars RotationThe Cullars Rotation is an ongoing agricultural experiment focusing on soil fertility that is located on the campus of Auburn University in Auburn, Lee County. It was named for J. A. Cullars, who with his brother-in-law J. P. Alvis began farming the land in the 1880s. The experimental plot was established in 1911 by the Alabama Agricultural Experiment Station and is home to the oldest continuously conducted soil fertility test in the southern United States; it is also the second-oldest cotton research experiment in the world, the oldest being the Old Rotation, also at Auburn University. The Cullars Rotation was placed on the National Register of Historical Places in 2003.

Early records at Auburn University suggest that Cullars and Alvis allowed biology professor George F. Atkinson of the Agricultural and Mechanical College of Alabama (now Auburn University) and others to conduct numerous early cotton fertility experiments on the property in the late 1800s. Atkinson's research on this site led to the discovery that cotton rust was caused by a deficiency of potassium. Atkinson reported his results in some of the earliest bulletins of the Alabama Agricultural Experiment Station in 1891 and 1892. This research played a role in the development of the fertilizer industry in the South. The Cullars Rotation experiment was established on this site to determine how much potassium and other nutrients were needed to sustain crop production. Crop yield data from the Cullars Rotation has been used over the years to support fertilizer recommendations for crops as well as the continuance of the soil testing program that began at Alabama Polytechnic Institute in 1953. Current research focuses on the nutrient requirements for sustaining and increasing crop production on lands that have been continually farmed for more than 100 years.

In 1911, the Alabama Legislature appropriated funds for the Alabama Agricultural Experiment Station (AAES) to conduct farm-based research throughout the state. AAES soon established some 226 experiments on farmers' fields throughout the state. The Cullars/Alvis property was planted to conduct soil fertility tests for cotton, corn, and legumes. As with the Old Rotation, established in 1896, AAES director John F. Duggar was involved with the Cullars Rotation's creation, but records do not credit any single researcher with designing the experiment. The plot soon became known as the Alvis Field.

Cullars Rotation DiagramThe three-acre Cullars Rotation was designed primarily to study the long-term effects of fertilizer components (nitrogen, phosphorus, and potassium), lime, and other nutrients on crops in a three-year rotation. Plantings took place on plots that were 110 feet long and 20 feet wide and included cotton, corn, small grains such as oats and wheat, and summer legumes such as cowpeas, crotalaria, and soybeans. The fields were not irrigated and were dependent upon rainfall and soil moisture and remain so. Originally, eleven plots were given three treatments, one for each of the three crops in the three-year rotation, in an ordered block design. In 1914, three more plots (designated A, B, and C) were added to each block to include the effect of winter legumes in the experiments (Figure 1).

In 1938, John Alvis's daughters sold the land encompassing Alvis Field to Alabama Polytechnic Institute (as Auburn University was known by that time). Plot lengths were shortened to 99 feet in the 1950s to allow mechanical equipment to maneuver between the blocks. Prior to 1997, all plots were tilled with moldboard plowing, disking, and regular cultivation, with winter cover crops (known as green manures) being turned under each spring to add organic matter to the soil. Since 1997, however, all crops have been grown with minimum tillage and with genetically modified cultivars. Cotton and corn are planted directly into previous crop residue in narrow rows using minimum soil disturbance. Soybeans are drilled into wheat residue in June using a no-till seed drill. Thanks to the boll weevil eradication efforts, few insecticides have been needed for pest control. The current experiment is a three-year rotation of cotton followed by crimson clover, corn harvested for grain followed by winter wheat, and soybeans planted after a wheat harvest in June. All crops are machine harvested, but cotton and corn yield estimates are determined through hand-harvesting portions of each plot.

Cullars HIstoric MarkerThe Cullars Rotation provides researchers with a dramatic example of the effects of soil nutrients on crop production as well as the effects of droughts or excessive rain. Particularly dramatic are the plots, such as plot C, which have had no soil amendments since 1911. In addition, no potassium has been added to plot 6, no lime to plot 8, and no phosphorous to plot 2 (Figure 2-5). Long-term trends overall reveal periods of yield increases and dramatic decreases. Through the experiments, researchers have learned that corn and wheat can tolerate lower-than-ideal potassium levels and still produce a crop but cotton yields are drastically reduced by low soil potassium. Conversely, cotton can tolerate low levels of phosphorus that devastate corn and wheat yields. Most important, the Cullars Rotation has shown that good management and nutrient replacement can deliver high yields on plots cultivated over many years.

In 2000, the Jule Collins Smith Museum of Fine Art was constructed on most of the Alvis Field, but Auburn University preserved the section shown in the diagram as the Cullars Rotation for on-going research and demonstration of sustainable crop production for soils of the southern United States. The Cullars Rotation experiment continues to document long-term trends in non-irrigated crop yields and soil changes resulting from variable rates of soil treatments. It also provides a valuable and accessible teaching tool for monitoring crop nutrient deficiencies and a stable and controlled environment for allied studies.